Develop a reference doc contribution policy

[jbogarthyde]

UPDATE 05/27/2024 (transfer issue from in-toto/docs)

• Specify how and where developers provide reference docs for new implementations.
  Reference documentation should go with the implementation repo in GitHub, with sources and generation information in a doc subdirectory.
• Specify what to document for an implementation.
  Use the Python Reference Implementation's reference docs to see what needs to be documented.
  These are generated using source files and a makefile in the implementation's doc subdirectory.
• Add the policy to https://github.com/in-toto/community/blob/main/CONTRIBUTING.md

[lukpueh]

... with sources and generation information in a doc subdirectory.

There might be programming language-specific best practices for setting up reference documentation.

I think we don't need a policy for where a subproject hosts their docs, but instead recommend that a link to the docs should be included in project wide docs.

[Ayush9026]

@lukpueh sir will raise PR for this issue.

[DarikshaAnsari]

@lukpueh doc subdirectory link is broken